Under　the　incomplete　phase　operation　of　EHV　transmission　line　with　shunt　reactor　and　neutral　reactor　after　the　extinguishment　of　transient　fault　arc,　a　complex　circuit　with　shunt　reactor,　neutral　reactor,　distributed　capacitance　and　distributed　impedance　is　formed.　In　order　to　study　its　characteristics,　a　relative　accurate　transient　circuit　with　lumped　parameters　is　set　up　through　simplification,　for　which　the　Laplacian　equations　are　deduced　to　calculate　its　eigenvalues　and　obtain　its　operational　features.　Its　correctness　is　verified　by　the　comparison　with　ATP　simulation　results.　According　to　the　natural　component　frequency　calculated　by　proposed　method　for　the　faulty　phase　voltage,　its　natural　component　and　compulsive　component　are　extracted　and　their　ratio　can　be　used　as　the　criterion　for　arc　extinguishment　of　faulty　phase.